Method for forming pure metal or non-metal deposits

ABSTRACT

A method for forming pure metal or non-metal deposits, said method consisting in introducing, in the vapour state, at least one metal or non-metal fluoride of higher valence into an enclosure containing at least one substratum to be metal-coated and a source for providing the metal or non-metal to be deposited, heating said source in order that the higher-valence fluoride is transformed, when contacting said source, into at least one sub-fluoride which evaporates, is condensed on the substratum and is transformed into fluorine and into the metal, or the non-metal, which constitutes the desired deposit.

ueu 5R lO--7-75 QR United States Patent [191 Dejachy et al.

[451 v Oct. 7, 1975 METHOD FOR FORMING PURE METAL OR NON-METAL DEPOSITS[75] Inventors: Jacques Dejachy, Saint-Cloud;

Jacques Gillardeau, Longjumeau, both of France [73] Assignee:Commissariat a IEnergie Atomique,

Paris, France 22 Filed: Nov. 1,1973

21 Appl.No.:4l2,0l6

[30] Foreign Application Priority Data Nov. 7, I972 France 72.39334['52] U.S. Cl. 428/408; 427/237; 427/253;

427/255; 428/450; 428/457; 428/472 [51] Int. Cl. C23C 11/02 [58] Fieldof Search 117/106 R, 107.2 R

[56] References Cited UNITED STATES PATENTS 2,887,407 5/1959 Koch 1ll7/107 3,658,577 4/1972 Wakefield 117/106 R Primary Examiner-Harris A.Pitlick Attorney, Agent, or FirmCameron, Kerkam, Sutton, Stowell &Stowell 57 ABSTRACT 14 Claims, 2 Drawvin' g Figures US. Patent Oct.7,1975

METHOD FOR FORMING PURE METAL OR NON-METAL DEPOSITS The presentinvention relates to a method for obtaining metal or metal-like coatingsin the pure state from the high-valence corresponding fluorides.

It has already been possible to obtain metal coatings from metalfluorides by decomposing the latter in the vapour state, under a givenpressure and at a given temperature, on a substratum to be metallized,said substratum being itself of metal or of a material likely todecompose fluorides.

According to the above method, whenever a metal M is brought intocontact with its fluoride MFn (n being the valence of said metal) in thevapour state and at an appropriate temperature, there is formed on thesurface thereof a deposit of the fluoride metal, according to thefollowing reaction:

nF (adsorbed) Whenever a gaseous MF molecule impinges on the metalsurface, the impact is efficient: the metal atom is deposited and twofluorine atoms are chemically adsorbed.

The positioning of the metal atom in the surface lattice of the receivermetal occurs very quickly. The adsorbed two fluorine atoms are capableof moving under the conditions of the experiment, and the desorptionthereof, which proves to be one of the main factors governing thekinetics of the deposition, allows the metal surface to be permanentlyuncovered.

When a fluoride MF,,, in the vapour state and at an appropriatetemperature is in contact with a substratum that provides volatilefluorides, the fluorides obtained are eliminated and leave the metal inthe pure state.

When a fluoride MP in the vapour state and at an appropriate temperatureis in contact with a metal that does not provide volatile fluorides andthe pure metal obtained is soluble in the metal forming the substratum,alloys are obtained, which occurs, e.g., when the two metals involvedare platinum and copper. When a fluoride MF,,, in the vapour state andat an appropriate temperature, happens to be in the presence of asubstratum that does not provide volatile fluorides, and the substratumand the metal obtained are not miscible, it is possible to decompose thefluoride in contact with said substratum and then eliminate same with aview to obtaining pure metal.

The thus formed coatings are good, but they require a highly careful anduneasy preparation of the fluorides as used, which have to be thermallydecomposable in a direct way. It happens that some fluorides arehygroscopic to such an extent that their previous preparation apart fromthe vapour-deposition enclosure could not be resorted to, since theirhandling is, in fact, rendered impossible in view of their considerableinstability with respect to the traces of water which are always to befound on the sites of experiments.

Another method consists in reducing a fluoride by 1 means of hydrogen,and it also leads to good coatings,

while however showing major drawbacks.

In certain instances, e.g. when the geometry of the substratum to becoated prevents the easy renewal or 2 reagents, the excess hydrogen mayalter the hydrogen/- gaseous fluoride ratio to the point ofdeteriorating the metal deposit, or even causing the vapour-depositionto stop.

The presence of hydrogen leads to the production of hydrofluoric gas,and steps, generally considered as dangerous, have to be taken fordraining and storing said gas.

Too great a concentration of hydrofluoric gas in the vicinity of thesubstratum may, quite undesirably, lead to a reaction opposite to thedesired one, viz. the recombination of the metal deposited in thefluoride state.

The reduction method has therefore to be rejected whenever the geometryof the objects to be coated is complicated, or whenever it is desired toform deposits inside parts comprising many branches or, e.g., insidelong and narrow tubes.

A new method, free of the above drawbacks, has been discovered and it isbased on the thermal decomposition of a metal or non-metal sub-fluoride,obtained in situ by the reaction of the corresponding higher valencefluoride on the metal or the non-metal substance.

The invention relates to a method for forming pure metal or non-metaldeposits, said method consisting in introducing, in the vapour state, atleast one metal or non-metal fluoride of higher valence into anenclosure containing at least one substratum to be coated and a sourcefor providing the metal or non-metal to be deposited, heating saidsource in order that the higher valence fluoride is transformed, whencontacting said source, into at least one sub-fluoride which evaporates,is condensed on the substratum and is transformed into fluorine and intothe metal, or the non-metal, which constitutes the desired deposit.

It is well known that the fluorides of higher valence are fluoridizingand cannot be thermally decomposed until the metal is obtained. It isonly by means of the reduction of these fluorides with hydrogen that atotal chemical decomposition can be obtained. On the other hand, thesub-fluorides are not fluoridizing in general, and they can be thermallydecomposed on a hot substratum in order to provide the metal directly.

According to the invention, the formation of subfluorides and thethermal decomposition of same occur simultaneously. The formation of asub-fluoride, having the general formula MF froma higher fluoride,having the general formula MF,,, and the metal M is carried out asfollows:

In MF,

gas

n and m being the valences of the elements and n being higher than m.

By way of non limitating. examples, the following compounds can bementioned as fluorides of higher valence capable of providing athermally decomposable sub-fluoride: wF6, MoF6, ReF6, PtF6, TaFS, NbFS,BFS, TiF4, CF4, SiF4 In order to obtain the useful sub-fluoride, thehigher valence fluoride is caused to react on the corresponding metal ornon-metal, heated to the appropriate temperature. It is to be noted thatthe generating metal or non-metal can be very easily located in thevicinity of the part to be coated, which permits to form the subfluoridein the vicinity of the surface on which the de- MFm MFm- M mF- M Fadsorbed adsorbed adsorbed solid desorbed gas metal When a gaseousmolecule of sub-fluoride MF,, inpinges on the substratum to be coated,heated to the appropriate temperature, the impact is efficient and theMF, molecule is activated to a sufficient extent to be quickly absorbedby the substratum. The chemical adsorption being of a dissociatingnature, the sub-fluoride adsorbed decomposes into metal M and intofluorine atoms. The metal obtained is inserted into the surfacecristalline lattice, and fluorine is desorbed, which permits furthermolecules of sub-fluorides to be introduced and the vapour deposition toproceed. The method according to the invention can be illustrated, forexample, by the vapour deposition of tungsten (W). Hexafluoride WFreacts on tungsten metal W as follows:

SWF W--) 6 WF,,

gas metal gas When those two metals are different, reactions of thefollowing types will take place:

It can be noted that the tungsten hexafluoride used at the beginning ofthe reaction is re-generated at the end of that reaction; it thus actsas a catalyst. It is therefore possible to introduce the gas into theenclosure and to carry out the reaction under constant pressure.

The above reaction can be written as follows:

The metal fluoride MF or MP thus formed is then decomposed on thesuitably heated part to be coated, thus freeing the metal which isdeposited:

MF MF M F---) M F gas adsorbed adsorbed adsorbed metal desorbeddeposited or MF MF M 2F) M F gas adsorbed adsorbed adsorbed metaldesorbed deposited and the tungsten pentafluoride thus formed isthermally decomposed as follows:

5 WF5 WF5 W 5F -)W F gas adsorbed adsorbed adsorbed metal desorbed Theformation of sub-fluoride and the decomposition of said fluoride occursimultaneously provided the substratum to be coated and the sub-fluoridegenerating metal are heated to carefully chosen different temperatures.

A careful selection of these temperatures will permit not only to carryout the method but also to act favorably on the kinetics ofvapour-deposition and on the properties of the metal deposits obtained.

It can be noted that, in the particular instance of tungsten, very goodcoatings are achieved by raising the generating source to a temperatureof about 750F (400C) and the substratum to a slightly lower temperature.It can also be noted that similar results can be obtained by carryingout the reduction method, but, in the latter case, the temperature mustreach about 1290F (700C), leaving aside the already mentioned drawbacksof the method itself.

Two different cases can be contemplated, according as the source metaland the metal of the gazeous fluoride introduced into the reactionenclosure are the same or not.

When those two metals are identical, reactions of the following typeswill take place:

The fluorine provided by the thermal decomposition of MP or MPrecombines with Wlto give back fluoride WF i.e. the gaseous catalystwhich is thus regenerated.

A great many metal deposits can be obtained in this way. By way ofexample can be mentioned the copper deposits from CuF and CuF, and thenickel deposits from NiF and NiF. The following metals are transferedand vapour-deposited according to that method: iron, cobalt, zinc,silver, gold, cadmium, and aluminum, to mention only the most frequentlyused metals.

The above reaction has the advantage of permitting the vapour-depositionof metals such as, e.g., nickel, copper, aluminum, zinc, cadmium,zirconium, the fluorides of which, which are not volatile enough, cannotbe validly used in the other vapour-metallurgy methods.

The operating conditions and the results of several tests are summed upin the following table 1.

The method according to the invention has many others advantages.

It permits to obtain deposits of metals the fluorides of which are verypoorly volatile, and therefore can hardly be used, and even cannot beused at all, in the ordinary vapour metallurgy methods, in particular inthe reduction methods.

Since the gaseous phase contains no hydrogen, no hydrofluoric acid isformed, which might impair the formation of good deposits.

The method which consists in adsorbing the sub-fluorides molecules anddesorbing the fluorine atoms formed which ensure a self-regulation ofthe deposition speed, necessarily leads to good deposits, even whenoperating at temperatures which would beconsidered as too low, forinstance in a reduction method. It is thus possible to make metaldeposits on substrata which could no sustain high temperatures. Thedeposits obtained by means of the method according to the invention arecompact, even, adhesive and epitaxic,:whenever allowed by the nature ofthe substratum and of the deposit. a

A remarkable vapour-deposition technology. can be developed, takingaccount of the fact that the fluoride (MF or MP useful tothevapour-deposition, can be generated in the. vicinity of the surfaceto be coated, whatever be the shape of the latter; one has only to putthe metal source near the substratum. This is of considerable advantagefor carrying out depositions inside parts of various shapes such astubes, valves and containers. The shape of the part to be coated by nomeans impairs .the very good penetration power associated to the method.

With a view to carrying out said method properly, it is necessary thatthe metal generating source be hot enough for causing the usefulfluoride (MF or MF to vaporize and to be transferred to the substratumto be coated. I I

The metal generating member may be a wire or a bar, heated by Jouleeffect. The generatingsource may also be a rod, indirectly heated bymeans of a non-consumable thermal member, the shape of that rod beingadapted to each particular instance.

That rod may either be coated with the metal obtained by sin'tering, orconsist in a tank containing fragments of the metal to bevapour-deposited. I

In some devices for carrying out the above method, the part to be coatedis preferably directly heated by the metal member which generates metalM, and in this case a heat insulating member must surround said part.

The shape of the devices for carrying out the method according to theinvention varies according to the shape, the nature and the number ofthe articles to be coated.

The following description will provide two examples of the coating oftubes.

FIG. 1 is a section through a device for coating the inside of a tube,and

FIG. 2 is a section through a device for coating both the inner portionand the outer portion of a tube; as can be seen in FIG. 1, tube 1, madeof any metal alloy, the inside portion of which is to be metal coated,is introduced into a heat insulated sleeve 2, with a view to avoiding asbest as possible, heat-losses by radiation. A metal or non-metal rod 3is held by the ends thereof inside the tube at the level of plugs 4 and5. Plug 4 has an opening for conduct 6 through which a higher valencefluoride is introduced. For operating that device, the rod must beheated to a predetermined temperature before introducing, throughconduct 6, the fluoride which, by contacting bar 3, generates asub-fluoride that forms a deposit of the inner wall of tube 1.

In FIG. 2, the elements similar to those of FIG. 1 are given the samereference numerals. Tube 1 is held within an enclosure 7 by means ofbrackets (not shown). The arrangement as shown permits, as in theprevious instance, to coat the innerportion of tube 1 with metal, andalso permits to coat the outer portion of that tube, through theaddition of bars 3 and 3" which are metal canon-metal generating sourceslike bar 3, and of conducts-5' and 5" for the introduction of fluorine.It is to be specified thatsthe inner wall of enclosure 7 is of amaterial which is not likely to retain a metal deposit. 1 Y v r Inaddition to the fact'that it is carried out as explained abovewith no.generation of hyrogen and hydrofluoric gas, the method according to theinvention permits to. eliminate the fluorine generated during thedissociation of the sub-fluoride, by re-combining it with the sourcemetal. The reaction interface, and more exactly the composition of thegaseous phase, are therefore perfectly constant for all the duration ofthe vapour-deposition, whatever be the shape of the part to bemetal-coated. v

On account of the cristal growth whichfgoverns the deposition, viz. theadsorption of the sub-fluoride molecules and the desorption of thefluorine atoms generated through which .the deposition speed isselfregulated, the vapour-deposit is necessarily good. This is even thecase with deposits carried out at temperatures which would prove muchtoo low for the reduction method. It follows that the method accordingto the invention permits to coat materials likely to be definitivelyaltered at higher temperatures,,. O ine can mention, for instance, thecase of deposits made on metals subjected to allotropic transformationsat high temperatures and for which there is a risk of deteriorating thedeposit-substratum interface, at the moment of passing the allotropictransformation point, during the cooling step.

It must be pointed out that thedep osits obtained carrying outthemethodaccording to,,th e invention are both adhesive, compact andeven, and that their growth is carried out epitaxically, viz. thecristalline lattice 'develops atom per atom in agreement with thesurface cristalline lattice, which permits to obtain as desiredmonocristals having agiven orientation.

Such deposits'can be made on many various substrata, all the more as, asalready mentioned, the method accordingto the invention permits toobtain very good deposits at temperatures lower than those involved inknown methods.

Excellent tungsten deposits were obtained, from WP on the followingsubstrata, given merely as examples: tungsten, molybdenum copper,nickel, monel-metal, inconel, iron, graphite, silicon, alumina.

It is also to be noted that it is possible to make vapour-deposits withalloys. It is indeed possible to carry out the co-deposition of twometals, by taking advantage of the respective chemical natures of thegenerating metal and of the gaseous fluoride of higher valence. One canmention, by way of example, the excellent results acheived as regardsthe co-deposition of molybdenum and tungsten, starting with a generatingsource of tungsten and with molybdenum hexafluoride as the gas.

A remarkable vapour-deposition technology can be developed taking intoaccount the fact that sub-fluoride useful for the vapour-deposition canbe generated in the vicinity of the surface to be coated whatever be theshape of the latter. It is only sufficient to put the metal or non-metalsource near the substratum. This is of considerable advantage for makingdeposits e.g. inside tubes, even very long and narrow tubes, insidevalve bodies, complicated tubing, containers, etc The shape of themember to be coated by no means impairs the excellent penetrating powerassociated to the method.

The metal or non-metal source can be a wire or a bar, heated by Jouleeffect. That source can also be a rod directly heated by means of anon-consumable thermal member. The shape of that rod may be adapted toeach particular instance. The rod either can be coated with the metalobtained by sintering or according to any vapour-deposition method, orconsists in a tank containing metal fragments to be vapour-deposited.

In some devices for carrying out the method according to the invention,the part to be coated is preferably heated directly by the generatingmetal member, said part being surrounded by a heat-insulating member.

The invention may have quite a number of applications in the field ofelectronics, in particular for the manufacture of the transmitters ofelectronic-tungsten converters, and for the manufacture of X-ray tubesanticathodes and in particular, in the field of space research, formanufacturing titanium thermal shields. The following applications canalso be mentioned:

- internal coating of tubular parts of small diameter;

- manufacture of metal tubes by making a deposit on the inner portion oron the outer portion of supporting tubes which are later on withdrawneither mechanically or chemically;

the deposition of reflecting or semi-reflecting metal layers ofrefractory metal, e.g. of tungsten, tantalum, molybdenum, on refractorysubstrata, such as ruby or corundum, permitting to use them at hightemperatures; the deposition of refractory metals on various types ofglass, in view of the possibility of making the deposition at a lowtemperature; the deposition of various metals on substrata sensitive tohydrogen; the production of catalysts, by depositing metals having ahigh specific area.

What is claimed is:

1. A method for forming pure metal deposits, said method consisting inintroducing, in the vapour state, at least one metal or metalloidfluoride of higher valence selected from the group consisting of: WF MFReF PtF TaF NbF BF TiF SiF CF, into an enclosure containing at least onesubstratum to be metal-coated and a source of the metal to be depositedselected from the group consisting of nickel, copper, aluminum, zinc,cadmium, molybdenum, tungsten and zirconium, heating said source inorder that the higher valence fluoride is transformed, when contactingsaid source, into at least one sub-fluoride of the source metal whichcoats the substratum and is transformed into fluorine and into themetal, which constitutes the desired deposit.

2. A method according to claim 1, wherein the metal of the metalfluoride introduced in the vapour state is the same as the metal of thesource.

3. A method according to claim 1, wherein the metal of the metalfluoride introduced in the vapour state is different from the metal ofthe source.

4. A method according to claim 2, wherein the fluoride introduced in thevapour state is molybdenum hexafluoride, and wherein the source ismolybdenum.

5. A method according to claim 3, wherein the fluoride introduced in thevapour state is molybdenum hexafluoride and wherein the source istungsten.

6. A method according to claim 1, wherein the substratum is a materialselected from the group consisting of tungsten, molybdenum, copper,nickel, monel metal, inconel, iron, graphite, silicon and alumina.

7. A method according to claim 1, wherein the source is heated to atemperature above the substratum temperature.

8. A method according to claim 1, wherein the source of tungsten isheated to about 750F (400C).

9. A method according to claim 1, wherein the source is selected fromthe group consisting of an electrically heated wire or a hollow rod.

10. A method according to claim 9, wherein said rod is coated with ametal obtained by sintering or by vapour-deposition.

1 l. A method according to claim 9, wherein said hollow rod forms a tankcontaining fragments of the metal to be vapour-deposited.

12. A method according to claim 1, wherein said substratum is the innerwall of a tube, and the source and the fluorine inlet conduit arelocated within said tube.

13. A method according to claim 1, wherein said substratum is the outerwall of a tube, said source and fluorine inlet conduits being located,outside said tube, within an enclosure which does not retain the metaldeposit.

14. A product coated with metal deposits by the method of claim 1.

1. A METHOD FOR FORMING PURE METAL DEPOSITS, SAID METHOD CONSISTING ININTRODUCING, IN THE VAPOUR STATE, AT LEAST ONE METAL OR METALLOIDFLUROIDE OF HIGHER VALENCE SELECTED FROM THE GROUP CONSISTING OF: WF6,MOF6, REF6, PTF6, TAF5, NBF5, BF5, TIF4, SIF4, CF4 INTO AN ENCLOSURECONTAINING AT LEAST ONE SUBSTRATUM TO BE METAL-COATED AND A SOURCE OFTHE METAL TO BE DEPOSITED SELECTED FROM THE GROUP CONSISTING OF NICKEL,COPPER, ALUMINUM, ZINC, CADMIUM, MOLYBDENUM, TUNGSTEN AND ZIRCONIUM,HEATING SAID SOURCE IN ORDER THAT THE HIGHER VALENCE FLUROIDE ISTRANSFORMED, WHEN CONTACTING SAID SOURCE, INTO AT LEAST ONE SUB-FLUORIDEOF THE SOURCE METAL WHICH COATS THE SUBSTRATUM AND IS TRANSFORMED INTOFLUORINE AND INTO THE METAL, WHICH CONSTITUTES THE DESIRED DEPOSIT.
 2. Amethod according to claim 1, wherein the metal of the metal fluorideintroduced in the vapour state is the same as the metal of the source.3. A method according to claim 1, wherein the metal of the metalfluoride introduced in the vapour state is different from the metal ofthe source.
 4. A method according to claim 2, wherein the fluorideintroduced in the vapour state is molybdenum hexafluoride, and whereinthe source is molybdenum.
 5. A method according to claim 3, wherein thefluoride introduCed in the vapour state is molybdenum hexafluoride andwherein the source is tungsten.
 6. A method according to claim 1,wherein the substratum is a material selected from the group consistingof tungsten, molybdenum, copper, nickel, monel metal, inconel, iron,graphite, silicon and alumina.
 7. A method according to claim 1, whereinthe source is heated to a temperature above the substratum temperature.8. A method according to claim 1, wherein the source of tungsten isheated to about 750*F (400*C).
 9. A method according to claim 1, whereinthe source is selected from the group consisting of an electricallyheated wire or a hollow rod.
 10. A method according to claim 9, whereinsaid rod is coated with a metal obtained by sintering or byvapour-deposition.
 11. A method according to claim 9, wherein saidhollow rod forms a tank containing fragments of the metal to bevapour-deposited.
 12. A method according to claim 1, wherein saidsubstratum is the inner wall of a tube, and the source and the fluorineinlet conduit are located within said tube.
 13. A method according toclaim 1, wherein said substratum is the outer wall of a tube, saidsource and fluorine inlet conduits being located, outside said tube,within an enclosure which does not retain the metal deposit.
 14. Aproduct coated with metal deposits by the method of claim